7227301
| Question | Answer |
| What did Pasteur and Joubert do in 1877? | Growth of the anthrax bacilli inhibited when cultures contaminated with mould |
| Who discovered, partially refined and carried out successful testing on animals of a substance with antibiotic properties? (the substance was penicillin) | Ernest Duchesne 1897 |
| What did Alexander Fleming do in 1928? | Staphylococcus bacteria died in the vicinity of penicillium mould. |
| Who isolated and demonstrated anti-staphylococcus activity in mice? | Florey/Chain 1940 |
| Who carried out the first clinical trials of penicillin? | Charles Fletcher 1941 |
| Who won the 1945 Nobel Prize in Physiology or Medicine? | Fleming Chain Florey |
| What is a bacterium (brief outline). | Prokaryotic Single Cell Organism No membrane-enclosed nucleus Possess a cell wall |
| Describe the bacterial cell wall | Composed of layers of peptidoglycan (unique to bacterial cell walls) Peptidoglycan = cellulose-like structural polysaccharide. It is covalently bound to short peptide chains in layers. Transpeptide linkages are cross-linking 2 peptidoglycan strands (provide strength to the cell wall) |
| Explain what occurs during the cross-linking of two peptidoglycan strands. | A COOH group on one amino acid from the first peptidoglycan strand binds to a NH2 group on the second peptidoglycan forming a new peptide bond. This is the transpeptide linkage |
| Outline the enzymatic catalysis of peptidoglycan cross-linking. | 1st strand forms a reactive ester bond with an enzyme (serine residue in the active site of the enzyme). Enzyme = glycopeptide transpeptidase The amino group of the 2nd peptidoglycan strand attacks the reactive ester. The enzyme is released (free to catalyse further reactions) Transpeptide linkage is formed |
| There are many derivatives of penicillin. What do all penicillins share in common with regards to their structure? | Bicyclic ring R groups vary, depending on the medium on which the mould is cultured. |
| Give the 3D structure of penicillin. | Non planar molecule Half open book shape Well-defined structure (rigid) |
| Why are β lactam antibiotics reactive? | The β lactam ring = 4 membered cyclic amide, highly strained |
| Basic structure of β lactam antibiotices | β lactam ring 5 membered ring containing sulfur side chain (benzyl) |
| How does penicillin inhibit glycopeptide transpeptidase? | Penicillin mimics the topology of the terminal portion of the peptidoglycan. (structures are imposable, only difference is that penicillin is very rigid) Its well-defined shape is similar to (D)-Ala-(D)-Ala Reactive β lactam ring triggers a reaction with serine in the active site of the glycopeptide transpeptidase enzyme. Lactam bond breaks open and a new ester bond between the lactam and serine is formed. Ester bond in GPTas active site is stable, it cannot react with a 2nd peptidoglycan strand and is inactivated |
| What are the implications of β lactam antibiotics on the cell wall of bacteria? | Weak cell walls because no-crosslinking of peptidoglycan strands occurs. Bacteria cells become osmotically fragile. |
| Which type of bacteria is Penicillin G active against? | Gram positive |
| What are cephalosporins active against? | Gram positive and Gram negative bacteria |
| What is cephalosporin? | A β lactam containing molecule that reactions with the same mechanism as penicillin in the inhibition of glycopeptide transpeptidase |
| Structure of cephalosporin | β lactam ring (4 membered) + 6 membered ring containing sulfer |
| Difference between cephalosporins and penicillins structure? | Penicillin - 5 membered ring with sulfur Cephalosporins - 6 membered ring with sulfur (both have lactam rings) |
| What is the main mechanism of resistance against β lactam antibiotics? | The ability of bacteria to express β lactamases that can degrade penicilins |
| What are β lactamases? | They are mutated transpeptidases (mutated in the catalytic active site) They are produced in addition to transpeptidases to protect them from the action of β lactam antibiotics |
| How do β lactamases work to hydrolyse penicillin? | β lactamases have serine in their active sites (modified- are larger than active sites in transpeptidases). Serine forms an ester bond with the lactam ring in penicillin. Water can hydrolyse the ester bond (able to fit in) Penicillin is destroyed, β lactamase able to catalyse another reaction |
| What is the effect of β lactamases on penicillins and cephalosporins? | Hydrolysis of β lactam bonds Open β lactam rings Half open book shape lost |
| What is a solution to resistance to β lactam antibiotics? | Clavulanic acid - Tandem Drugs |
| Outline the structure of clavulanic acid | β lactam ring 5 membered ring with oxygen |
| What is clavulanic acid? | A β lactamase inhibitor NOT a β lactam antibiotic It does not inhibit glycopeptide transpeptidase, it has no antibiotic activity by itself |
| What is a tandem drug? | A drug that contains β lactam antibiotic and a β lactamase inhibitor e.g. Augmentin |
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